Computed Tomography (hereinafter CT) is typically used in the diagnosis of tumors, hemorrhages and the localization of foreign objects within the human body. Additionally, CT can be used for qualitative imaging of abnormal pattens of blood flow. This technique could be especially useful for examination of the heart when myocardial infarction is known or suspected. In theory, the blood flow rate can be determined by injecting a contrast agent containing iodine or other high Z material into a person's vein, and then making a series of rapid x-ray computer tomography images of the heart. The resulting images could then be used to determine which parts of the heart are properly perfused with blood and the blood flow rate.
In practice, this technique cannot be used because of a phenomenon known as "beam hardening". Beam hardening occurs when more than one type of material is present in a scanned region, each of which have different energy dependent attenuation coefficients. Accordingly, the energy spectrum of the x-ray beam used to scan the patient is altered as the beam penetrates the patient's body. Because of the difference in energy spectra, the resulting images show distortions or so called "artifacts" that make interpretation of the images difficult.
While the beam hardening effect is routinely corrected in commercial CT scanners on the assumption that all materials in the body are approximately equivalent to water in their x-ray absorption characteristics, this assumption is known to be false, especially with regard to bones and iodine contrast agent. Accordingly, commercial CT scanners cannot compensate correctly for artifacts created by bone and iodine when both bone and iodine are present.
Thus, it would be desirable to have a method of correcting CT images to compensate for the artifacts created by bone and iodine when both bone and iodine are present.